1. Field of the Invention
This invention relates to electrical switching apparatus having an arc runner, which transfers the arc from separable contacts, such as arcing contacts, to an arc chute where the arc is extinguished.
2. Background Information
Electrical switching apparatus for power distribution systems include devices such as, for instance, circuit breakers, network protectors, transfer switches and disconnect switches. Power circuit breakers are typically used to connect a power distribution network to a power source. Such power circuit breakers must be able to withstand high currents for a period of time without tripping to give circuit breakers in the network time to respond and isolate the fault thereby localizing disruption of service. Thus, by the time the power circuit breaker responds, it may have to interrupt a sizable current. This results in the drawing of an arc as the circuit breaker contacts open. It is known to provide an arc chute adjacent to the opening path of the circuit breaker contacts. The arc chute is constructed of a number of spaced apart plates extending transverse to the arc. As the contacts open, the arc is transferred by electromagnetic forces to the arc plates, which cool the arc and increase the arc voltage by breaking it up into sections, both of which help to extinguish the arc.
It is known to employ an arc runner to drive an arc from a stationary contact to an arc chamber. See U.S. Pat. No. 4,229,630.
Typically, an arc is formed on the arcing contact and travels across a joint to the arc runner. At low currents, the electromagnetic force on the arc may not be adequate to force the arc to cross this joint. One end of the arc may remain on the stationary arcing contact, severely eroding the contact. If the arc does not move onto the arc runner it will not reach the arc chute in time for the breaker to interrupt.
U.S. Pat. No. 5,969,314 discloses an air circuit breaker with multiple movable arcing contacts, in which an arc runner is employed above an integral stationary arcing contact in order to provide a surface for the arc to run toward the center of the arc chute. This elongates the arc, divides it among the arc plates and cools the arc gases, thereby extinguishing the arc and interrupting current flow. The arcing contacts at the center of the arc chamber part last when the circuit breaker opens, causing the arc to form in the center of the arc runner. When the arc is created on the stationary arcing contact, it is more likely to travel along a sharp edge or corner of the part. A longitudinal vertical slot is disposed into the center of the arc runner in order to provide an attractive edge for the arc to travel toward the center of the arc chute. The edge of the slot encourages the arc to travel up the center of the arc runner, engaging the arc chute near the center and extinguishing the arc sooner. However, this center slot is no more attractive to the arc than the outside edges of the arc runner.
The arc may be attracted to the laterally extending edge of the stationary arcing contact instead of the slot in the arc runner. At higher voltages and lower current levels (e.g., as encountered in single-pole interruption testing for IEC certification), the arc has less electromagnetic drive to enter the arc chute and is more difficult to interrupt. The arc may run to one edge of the stationary arcing contact. This may prevent the arc from running up the arc runner. The arc may move to one side of the arc chamber and be less likely to enter the arc plates, possibly resulting in failure to interrupt.
There is a need, therefore, for electrical switching apparatus with an improved arrangement for extinguishing arcs generated during current interruption.
There is a more specific need for such an improved arrangement for directing the arc from the stationary arcing contact into an arc chute.
There is a still more specific need for such an improved arrangement for attracting the arc to the center of the arc runner and providing an improved path for the arc to follow to the center of the arc chute without stalling or wandering toward the sides of the arc chamber.
These needs and others are satisfied by the invention, which is directed to electrical switching apparatus in which a circuit breaker arc runner includes a longitudinal elongated raised ridge. The elongated raised ridge is preferably positioned directly above the location of arc formation and provides a prominence for concentrating electrical charge. This structure holds the arc in the center of the arc runner by providing the shortest path for the arc. The elongated raised ridge also provides a smooth elevated path that the arc follows up the height of the arc runner into the center of arc chute.
As one aspect of the invention, an electrical switching apparatus comprises: a load terminal and a line terminal; at least one pair of separable contacts electrically connected between the load conductor and the line conductor; an operating assembly adapted for movement between an open position and a closed position to open and close the separable contacts; an arc chute positioned adjacent the separable contacts; and an arc runner electrically connected to one of the separable contacts and extending toward the arc chute to provide a path for an arc struck between the separable contacts as the separable contacts open with movement of the operating assembly from the closed position, the arc runner having a longitudinal elongated raised ridge generally laterally centered.
The stationary arcing contact and the arc runner may comprise an electrically conductive member having a base surface in contact with the line terminal, a stationary contact surface forming the stationary arcing contact, and a runner surface leading toward the arc chute.
Preferably, the raised ridge includes a raised portion above the runner surface and a tapered portion which descends to a position proximate a surface between the stationary contact surface and the runner surface. The tapered portion may be above the stationary contact surface.
Alternatively, the raised ridge may include a raised portion above the runner surface and a tapered portion which descends to the stationary contact surface. The tapered portion may be flush with the stationary contact surface.
Alternatively, the raised ridge may include a raised portion above the runner surface and a proud portion, which protrudes above a surface between the stationary contact surface and the runner surface and above the stationary contact surface.
Alternatively, the raised ridge may include a raised portion above the runner surface and a tapered portion, which descends to a position which is offset from the stationary contact surface. The position, which is offset from the stationary contact surface, may be a position on the runner surface.
Preferably, the stationary contact is integral with the arc runner, thereby eliminating a joint therebetween.
As another aspect of the invention, an electrical switching apparatus comprises: a load conductor and a line conductor; a pair of main contacts including a movable main contact and a stationary main contact, and a separable pair of arcing contacts, including a movable arcing contact and a stationary arcing contact, the stationary main contact and the stationary arcing contact being in electrical contact with the line conductor; an operating assembly electrically connecting the movable main contact and the movable arcing contact to the load conductor, the operating assembly adapted for movement between an open position and a closed position to open and close the separable pairs of contacts, and also adapted for transitioning from closure of both the pair of main contacts and the separable pair of arcing contacts, to closure of only the separable pair of arcing contacts while the pair of main contacts are opened, to opening of the separable pair of arcing contacts in the open position thereof; an arc chute positioned adjacent the operating assembly; and an arc runner electrically connected to the stationary arcing contact and extending toward the arc chute to provide a path for an arc struck between the separable pair of arcing contacts as the separable pair of arcing contacts open with movement of the operating assembly from the closed position, the arc runner having a longitudinal elongated raised ridge generally laterally centered.
As a further aspect of the invention, an electrical switching apparatus comprises: a housing; a load conductor and a line conductor mounted in the housing; a pair of main contacts including a movable main contact and a stationary main contact, and a separable pair of arcing contacts, including a movable arcing contact and a stationary arcing contact, the stationary main contact and the stationary arcing contact being in electrical contact with the line conductor; a moving conductor assembly electrically connecting the movable main contact and the movable arcing contact to the load conductor and comprising a contact carrier mounted for movement between an open position and a closed position to open and close the separable pairs of contacts, at least one contact finger pivotally mounted on the contact carrier and having the movable arcing contact adjacent a free end and the movable main contact spaced from the free end, and contact spring means pivotally biasing the at least one contact finger to move from closure of only the pair of main contacts with the carrier in the closed position, to closure of both the pair of main contacts and the separable pair of arcing contacts, to closure of only the separable pair of arcing contacts while the pair of main contacts are opened, to opening of the separable pair of arcing contacts as the carrier moves to the open position; an arc chute positioned adjacent the moving conductor assembly; and an arc runner electrically connected to the stationary arcing contact and extending toward the arc chute to provide a path for an arc struck between the separable pair of arcing contacts as the separable pair of arcing contacts open with movement of the moving conductor assembly from the closed position, the arc runner having a longitudinal elongated raised ridge generally laterally centered.